JP2010537375A - LCD backlight with LED phosphor - Google Patents

Abstract

  The present invention relates to a semiconductor diode and a phosphor layer composed of a combination of at least two phosphors, wherein at least one phosphor emits red light and at least one phosphor emits green light. The present invention relates to a liquid crystal display including a backlight system having a white light source, and a method for manufacturing the same.

Description

  The present invention includes a phosphor layer comprising a semiconductor diode and a combination of at least two phosphors, wherein at least one phosphor emits red light and at least one phosphor emits green light. The present invention relates to a liquid crystal display provided with a backlight system having a white light source. The invention further relates to a backlight system and a method for manufacturing the same.

  Liquid crystal displays (LCDs) are passive display systems, i.e., they themselves do not emit light. These displays are based on the principle of whether light passes through a liquid crystal layer. This means that an external light source is required to produce the image. In a reflective liquid crystal display, ambient light is used as an external light source, which means that in principle, no backlight is required. In a transmissive liquid crystal display, light is generated in a backlight system. On the other hand, transflective liquid crystal displays (which are both transmissive and reflective at the same time), where the reflector is located behind a polarizer that is generally oriented away from the viewer, also play an even more important role. Fulfill. Each pixel here is divided into a reflective sub-pixel and a transmissive sub-pixel, and their associated liquid crystal layer thickness is approximately the ratio 1: 2. The reflective part functions with external light and has a reflective substrate layer, for example made of aluminum. The transmissive part functions in the same way as, for example, a TN (= twisted nematic) cell, and in particular in the case of poor external light conditions, the required contrast can be achieved by a backlight that can be switched on. The latter are used today, for example, in PDA, game (game boy), viewfinders for digital cameras, or (cheap) notebooks because they are particularly power-saving.

  In a liquid crystal display, the primary color of the pixel is generated by filtering the white light from the backlight, for example, with the aid of a color filter to blue, green and red. The color space that a display that is important for color display can produce is limited by the purity of the primary colors of blue, green and red. Expressed in the CIE xy chromaticity diagram, the red, green and blue primaries of the display form a triangle that indicates the color space that can be displayed by the display. Colors outside this color space are not displayed on the display.

In a liquid crystal display, the color space is determined by a number of factors.
The first is the light source for the backlight and the structure of the LCD panel itself: each pixel of the screen consists of red, green and blue regions. The colors of these regions are generated by transmission of white light from the backlight through the color filter unit. The color filter is one of the determinants for the display color space. Wide-band fluorescent light sources such as CCFLs (cold cathode fluorescent lamps = Hg low-pressure cold cathode discharge lamps) or xenon discharges that emit a broad color spectrum with undesired color components such as orange, yellow and cyan, for example Usually used for LCD backlight. In order to maximize the color space that can be displayed by the screen, only the highest purity red, green and blue are required. Since white light from the primary light source is subdivided into primary colors by the color filter, the primary colors must be saturated.

  In order to expand the color space, in this case it is necessary to convert the light from the backlight into a spectrum containing narrower bands of blue, green and red components through the use of additional color filters. In addition to the technical complexity of this type of additional color filter, the luminous flux here is greatly reduced, reducing the brightness of the screen.

  Thus, to avoid these disadvantages of broadband backlights, the additional complex color filters have replaced the CCFL resulting in a constrained color space and reduced screen brightness with LED arrays. These arrays consist of blue, green and red LEDs that emit a much narrower spectrum compared to the CCFL. For this reason, only a simple color filter is required, so the color space that can be displayed by the display is larger and the achievable brightness is greater. A further advantage arising therefrom is the higher energy efficiency of the display, since the backlight transmission (70%) in the LED is significantly greater than the CCFL (5%). In addition, LED backlights have a significantly longer life than CCFLs (100,000 operating hours in the case of LEDs compared to 5000 operating hours in the case of CCFLs) and are inevitable in CCFLs. Mercury is not used in LEDs.

  However, the disadvantage in the case of the use of blue, green and red LEDs for the backlight is that the semiconductor chips of the LEDs are different: InGaN is adopted for blue light and InGaN is similar (but Adopted for green light (with higher In content), and InGaAlP has been adopted as the basis for materials for red light. These three materials exhibit different efficiencies for light emission and have different degradation behaviors. As a result, it is necessary to employ a complex active control system that constantly maintains the color point of white light consisting of blue, green and red LEDs via a control circuit engaged in LED addressing.

This complex active control system for each individual LED (up to thousands of LEDs) in the backlight is 4 to 10 times more expensive for LCD TV screens with it than screens with CCFLs High cost is brought about.
The high price hinders market penetration of much better qualitative LED backlights.

  WO 02/095791 is a liquid crystal screen provided with a gas discharge lamp (cold cathode lamp or Xe discharge lamp) as a white light source, including a phosphor layer containing a combination of phosphors emitting red, green and blue light Is described.

  The object of the present invention was to provide a backlight system with the same high quality (with respect to displayable color space and brightness) as an R, G, B LED backlight, but at a significantly lower cost.

  Surprisingly, with regard to the use of specific LEDs, it is possible to omit the use of complex active control systems for each individual LED, and that these LEDs can be employed in conventional backlight systems. Found by the invention. These LEDs of the present invention allow for less expensive backlights that are calculated with respect to screen life and associated with lower costs than conventional CCFL backlights.

  Accordingly, the present invention is a liquid crystal display, wherein at least one semiconductor diode, preferably a blue light emitting semiconductor diode, and a combination of at least two phosphors, wherein at least one phosphor emits red light, And a liquid crystal display comprising at least one backlight system having a white light source comprising at least one phosphor layer comprising: and at least one phosphor emits green light.

FIG. 1 shows a schematic representation of the liquid crystal display (direct lighting design) of the present invention. (1 = LCD unit without backlight, 2 = backlight unit, 3 = diffuser, 4 = LED with the phosphor layer of the present invention, 5 = uniform light flux from the backlight unit). FIG. 2 shows a schematic representation of the liquid crystal display (side illumination design) of the present invention. (1 = LCD unit without backlight, 2 = backlight unit, 3 = diffuser, 4 = LED with the phosphor layer of the present invention, 5 = uniform light flux from the backlight unit).

  A liquid crystal display usually has a liquid crystal unit and a backlight system. The liquid crystal unit typically includes a liquid crystal cell having a first polarizer and a second polarizer and two transparent layers each with a matrix of light transmissive conductors. The liquid crystal material is disposed between the two substrates. Examples of the liquid crystal material include TN (twisted nematic) liquid crystal, STN (super twisted liquid crystal), DSTN (double super twisted liquid crystal), FSTN (foil super twisted nematic), VAN (vertical alignment) liquid crystal, or OCB (optical). Compensated bending) including liquid crystal. The liquid crystal cell is surrounded by two polarizers in a sandwich manner so that the second polarizer can be seen by the viewer.

Also, IPS (in-plane switching) technology is extremely highly suitable for monitoring applications. In contrast to the TN display, the conductor in the electric field where the liquid crystal molecules are switched is only located on one side of the liquid crystal layer in the IPS cell. The resulting electric field is uniform and is roughly arranged parallel to the substrate surface. The molecules are correspondingly switched in the substrate plane (in-plane), which results in a significantly lower transmission intensity viewing angle dependence compared to TN displays.
Furthermore, a lesser known technique for superior optical properties over a wide viewing angle is the FFS technique and its advanced fringe field switching (AFFS) technique. It has the same functional principle as IPS technology.
The invention further relates to a backlight system having a white light source comprising a semiconductor diode, preferably a blue light emitting semiconductor diode, and a phosphor layer comprising a combination of at least two phosphors emitting red and green light.

  The backlight system of the present invention may be, for example, a “direct illumination” backlight system (see FIG. 1) or a “side illumination” backlight system (see FIG. 2) having an optical waveguide and an output coupling structure. The backlight system has a white light source, which is usually located in the housing, preferably it has a reflector on the inside. Furthermore, the backlight system may have at least one diffusion plate.

  In order to generate and display a color image, the liquid crystal unit is provided with a color filter. The color filter includes pixels in a mosaic-like pattern that transmits either red, green or blue light. The color filter is preferably disposed between the first polarizer and the liquid crystal cell.

The white (primary) light source is blue light emitting indium aluminum gallium nitride, in particular represented by the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1. It is what is done. Preferably, the InGaN semiconductor diode emits white light or pseudo white light in combination with a corresponding conversion phosphor. This InGaN semiconductor diode has a maximum emission between 430 and 480 nm and has a very high efficiency and long life (> 150,000 hours) with only a slight efficiency degradation.

In a further aspect, the white light source can also be a light emitting compound based on ZnO, TCO (transparent conductive oxide), ZnSe or SiC.
In principle, a wide variety of designs selected depending on the application are possible for blue light emitting semiconductors that generate white light in combination with a phosphor layer.
According to the present invention, the white light source has a phosphor layer that includes a combination of red and green light emitting phosphors.

The invention further relates to a method of manufacturing a liquid crystal display with a backlight system having a white light source, which method comprises the following steps:
Blue light emitting InGaAlN semiconductors, in particular those represented by the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1, and red and green light emitting phosphors Producing at least one LED constructed from phosphor layers comprising the combination;
Providing a backlight system including a diffuser and a reflector by installing one or more LEDs in a housing;
Combining a backlight system with a corresponding liquid crystal unit including a front plate with a color filter system to provide a liquid crystal display.

The green light emitting phosphor is excited by a blue light emitting primary light source, but has a maximum light emission between 520 and 550 nm. Preferred in the present invention are all cerium (III) or europium (II) active phosphors selected from the group of thiogallate, silicate, oxonitridosilicate, aluminate, nitride or garnet. . Examples of these phosphors include (Y, Lu) ₃ (Al, Ga) ₅ O ₁₂ : Ce; SrSi ₂ N ₂ O ₂ : Eu; SrGa ₂ S ₄ : Eu; (Sr, Ba) 2S _i O ₄ : Eu and SrAl ₂ O ₄ : Eu can be mentioned here.

  They are also prepared via solid phase synthesis by conventional methods or by wet chemical methods (see William M. Yen, Marvin J. Weber, Inorganic Phosphors, Compositions, Preparation and optical properties, CRC Press, New York, 2004). Is done.

The red-emitting phosphor is preferably a line emitter and is excited by a blue-emitting primary light source or by a green-emitting phosphor. The red-emitting phosphor is preferably a europium (III) or chromium (III) activated line emitter. According to the invention, it has either a maximum emission between 590 and 620 nm (Eu (III) activated phosphor) or a maximum between 680 and 700 nm (in the case of Cr (III) activated phosphor). The phosphor layer is particularly preferably a red light emitting phosphor such as Al ₂ O ₃ : Cr, Na _0.5 Gd _0.3 Eu _0.2 WO ₄ , Na _0.5 Y _0.4 Eu _0.1 MoO _4. , Na _0.5 La _0.3 Eu _0.2 WO ₄ , Na _0.5 La _0.3 Eu _0.2 MoO ₄ , Na _0.5 La _0.3 Eu _0.2 (WO ₄ ) _0.5 (MoO ₄ ) _0.5 , La _1.2 Eu _0.8 MoO ₄ , La _1.2 Eu _0.8 WO ₄ , (Gd _0.6 Eu _0.4 ) ₂ (WO ₄ ) _1.5 PO ₄ A europium or chromium activated line emitter selected from the group of

Al ₂ O ₃ : Cr (ruby) is efficiently induced in the yellow-green region of the spectrum and emits a dark red line at 693 nm. Eu (III) activated phosphors can be employed when the use is made with a matrix that allows (partially) the forbidden internal ff absorption transition of europium.

Preferred red line emitters Al ₂ O ₃ : Cr (rubies) according to the invention can be prepared by wet chemical methods (see DE 102006054328.9 and DE 102007001903.5). These rubies are consequently manufactured very inexpensively and are suitable as pcLED conversion phosphors for the production of warm white light with high efficiency and excellent color reproduction with dark red emission. These phosphors can be prepared in a wet chemical process, resulting in Al ₂ O ₃ particles implanted with 0.01 to 10% by weight of Cr ³⁺ or Cr ₂ O ₃ , which can be prepared in size and unified morphology. Have

  The starting material for phosphor preparation consists of a base material (eg, an aluminum salt solution) and at least one chromium (III) containing dopant. Suitable starting materials are metals, metalloids, transition metals and / or rare earth nitrates, carbonates, bicarbonates, hydrogen phosphates, phosphates, carboxylates, alcoholates, acetates, oxalates, halogens Compounds, sulfates, organometallic compounds, hydroxides and / or oxides, which are dissolved and / or suspended in inorganic and / or organic liquids. Preference is given to using mixed nitric acid solutions, chlorides or hydroxide solutions containing the corresponding elements in the required stoichiometric proportions.

  A further advantage of the red-emitting phosphor of the present invention is that the emission of the phosphor increases with increasing temperature. This is surprising because the phosphor emission usually decreases with increasing temperature. This advantageous property of the present invention is particularly important when using phosphors in high power LEDs (> 1 watt energy consumption) because it is possible to reach operating temperatures higher than 150 ° C.

  Wet chemical preparation generally has better uniformity with respect to the stoichiometric composition, particle size and morphology of the particles from which the red line emitter of the present invention is prepared. The wet chemical preparation of the phosphor is preferably carried out by precipitation and / or sol-gel methods.

  The line emitters of the present invention are prepared by conventional methods from the corresponding metal and / or rare earth salts, preferably from aluminum sulfate, potassium sulfate, sodium sulfate and chromium alum solutions. The preparation method is described in detail in EP 763573.

  The phosphor or its precursor is applied here to the ruby particles under process conditions known to those skilled in the art. After separation from the suspension, the material is dried and subjected to a number of steps and a calcination process which can be carried out under reducing conditions at temperatures up to (partially) 1700 ° C. After multiple purification steps, the phosphor is fired for many hours at a temperature of 600 ° C to 1800 ° C, preferably 800 ° C to 1700 ° C. The phosphor precursor is now converted into the actual phosphor.

  It is preferred that the calcination be carried out at least partially under reducing conditions (eg using carbon monoxide, forming gas, pure or diluted hydrogen or at least vacuum or oxygen-deficient atmosphere).

  Furthermore, the red line emitters of the present invention can also be prepared by single crystal synthesis methods (for example, by the Bernoulli method, Kontakte (Merck) 1991, No. 2, 17-32 or Ullmann (4.) 15, 146, Source: CD Roempp Chemie Lexikon [CD Roempp's Lexicon of Chemistry]-Version 1.0, Stuttgart / New York: Georg Thieme Verlag 1995).

  The described method is used as hydrothermal synthesis under the names of Kilopros, Bridgeman-Stockburger, Czochralski, Bernoulli method and the like. A distinction is also made between crucible-free zone melting and crucible drawing (Source: CD Roempp Chemie Lexikon [CD Roempp's Lexicon of Chemistry]-Version 1.0, Stuttgart / New York: Georg Thieme Verlag 1995).

Red light emitting line emitter Na _0.5 Gd _0.3 Eu _0.2 WO ₄ , Na _0.5 Y _0.4 Eu _0.1 MoO ₄ , Na _0.5 La _0.3 Eu _0.2 WO ₄ , Na _0.5 La _0.3 Eu _0.2 (WO ₄ ) _0.5 (MoO ₄ ) _0.5 , La _1.2 Eu _0.8 MoO ₄ , La _1.2 Eu _0.8 WO ₄ , (Gd _0.6 Eu _0.4 ) ₂ (WO ₄ ) _1.5 PO ₄ is preferably prepared by wet chemical methods and continuous heat treatment (reference DE 102006027026.6). Starting materials that can be employed for the preparation are the corresponding metal, metalloid, transition metal and / or rare earth nitrates, halides and / or phosphates.

  According to the invention, the dissolved or suspended starting material is heated together with a surfactant, preferably glycol, for a long time and the resulting intermediate is separated at room temperature using an organic precipitating agent, preferably acetone. The After purification and drying of the intermediate, the latter is subjected to a heat treatment at a temperature between 600-1200 ° C. for a long time, resulting in a red line emitter phosphor as the final product.

  The phosphor layers, both red-emitting and green-emitting conversion phosphors, are chemically stable to degradation during LED operation, i.e., they tend to undergo hydrolysis and reaction with substances from their environment. Not shown.

  The examples that follow are intended to illustrate the invention. However, they should not be recognized as limitations at all. All compounds or components that can be used in the compositions are known and commercially available or can be synthesized by known methods.

Examples Example 1: Preparation of red emitting phosphor particles of composition Al _1.991 O ₃ : Cr _0.009 223.8 g aluminum sulfate 18 hydrate, 114.5 g sodium sulfate, 93.7 g potassium sulfate and 2 .59 g of KCr (SO ₄ ) ₂ × 12H ₂ O (Chromium alum) dissolves in 450 ml of deionized water at about 75 ° C. 2.0 g of 34.4% titanium sulfate solution is added into this mixture, resulting in an aqueous solution (a).
0.9 g of trisodium phosphate dodecahydrate and 107.9 g of sodium carbonate are dissolved in 250 ml of deionized water to produce an aqueous solution (b).
Two aqueous solutions (a) and (b) are simultaneously added to 200 ml of deionized water with stirring for 15 minutes. The mixture is stirred for an additional 15 minutes. The resulting solution is evaporated to dryness and the resulting solid is calcined at about 1200 ° C. for 5 hours. Add water to wash away free sulfate. Conventional purification steps with water and drying _{yield the} desired phosphor Al _1.991 O ₃ : Cr _0.009 .

Example 2: Red phosphor Na _0.5 Gd _0.3 Eu _0.2 WO ₄
2.708 g gadolinium nitrate hexahydrate and 1.784 g europium nitrate hexahydrate are dissolved in 100 ml ethylene glycol [solution 1]. At the same time, a solution of 1.550 g sodium tungstate dihydrate in 50 ml deionized water is prepared [Solution 2]. 40 ml of solution 1 is initially introduced and a mixture of 45 ml of solution 2, 45 ml of ethylene glycol and 3 ml of NaOH solution (1M) is added dropwise thereto. After the dropwise addition (the solution has a pH of 7.5), the mixture is heated under reflux for 6 hours. After cooling the reaction solution, 200 ml of acetone are added dropwise, the precipitate is then centrifuged off, washed again with acetone, dried in a stream of air, transferred onto a porcelain dish and 600 Bake at 5 ° C. for 5 hours.

Example 3: Preparation of red phosphor Na _0.5 Y _0.4 Eu _0.1 MoO ₄ 3.06 g of yttrium nitrate hexahydrate and 0.892 g of europium nitrate hexahydrate in 100 ml of ethylene glycol Dissolve [Solution 1]. At the same time, a solution of 1.210 g sodium molybdate dihydrate in 50 ml deionized water is prepared [Solution 2]. 20 ml of solution 1 is initially introduced and a mixture of 45 ml of solution 2, 45 ml of ethylene glycol and 3 ml of NaOH solution (1M) is added dropwise thereto. After the dropwise addition, the mixture is heated at reflux for 6 hours. After cooling the reaction solution, 200 ml of acetone are added dropwise and the precipitate is subsequently removed by centrifugation, washed again with acetone and dried in a stream of air.
The batch is transferred into a muffle furnace and baked at 600 ° C. for 5 hours.

Example 4: Preparation of red phosphor Na _0.5 La _0.3 Eu _0.2 WO ₄ (precipitation reaction)
2. 120 g of lanthanum chloride hexahydrate and 1.467 g of europium chloride hexahydrate are dissolved in 100 ml of deionized water [Solution 1]. At the same time, a solution of 4.948 g sodium tungstate dihydrate in 100 ml deionized water is prepared [Solution 2]. 100 ml of solution 1 is first introduced and solution 2 is added dropwise thereto (detection pH should be in the range of 7.5-8, if necessary adjusted with NaOH solution (1M) ). The mixture is then heated at reflux for 6 hours. After cooling the reaction solution, the precipitate is filtered off with suction and dried to produce a white precipitate.
The batch is fired at 600 ° C. for 5 hours.

Example 5: Preparation of red phosphor Na _0.5 La _0.3 Eu _0.2 MoO ₄ by complexation with citric acid 1.024 g of molybdenum (IV) oxide is gently heated to 10 ml of H ₂ O ₂ Dissolve in (30%). 4.608 g of citric acid is added to the yellow solution along with 10 ml of distilled H ₂ O.
1.040 g La (NO ₃ ) × 6H ₂ O and 0.714 g Eu (NO ₃ ) × 6H ₂ O and 0.340 g NaNO ₃ are also subsequently added so that the mixture is 40 ml.
The yellow solution is dried in a vacuum drying shelf, a blue foam is first formed from which a blue powder is finally produced. The solid is then calcined at 800 ° C. for 5 hours.

Example 6: Preparation of red phosphor Na _0.5 La _0.3 Eu _0.2 (WO ₄ ) _0.5 (MoO ₄ ) _0.5 2. 120 g of lanthanum chloride hexahydrate and 1.467 g of chloride Europium hexahydrate is dissolved in 100 ml of deionized water [Solution 1]. At the same time, a solution of 1.815 g sodium molybdate dihydrate and 2.474 g sodium tungstate dihydrate in 100 ml deionized water is prepared [Solution 2]. 100 ml of solution 1 is initially introduced and solution 2 is added dropwise thereto (pH should be in the range 7.5-8, adjusted if necessary with NaOH solution (1M)) . The mixture is then heated under reflux for 6 hours. After cooling the reaction solution, the precipitate is filtered off with suction, dried and the batch is then calcined at 600 ° C. for 5 hours.

Example 7: Preparation of red phosphor La _1.2 Eu _0.8 MoO ₄ by complexation with citric acid 1.024 g of molybdenum (IV) oxide is gently heated to 10 ml of H ₂ O ₂ (30%) Dissolve in. 4.608 g of citric acid is added to the yellow solution along with 10 ml of distilled H ₂ O.
1.040 g La (NO ₃ ) × 6H ₂ O and 0.714 g Eu (NO ₃ ) × 6H ₂ O and 0.340 g NaNO ₃ are also subsequently added so that the mixture is 40 ml.
The yellow solution is dried in a vacuum drying shelf, a blue foam is first formed from which a blue powder is finally produced. The solid is then calcined at 600 ° C. for 5 hours.

Example 8: Preparation of red phosphor La1.2Eu0.8WO4 by complexation with citric acid 0.9711 g of tungsten (IV) oxide is gently heated and dissolved in 10 ml of H ₂ O ₂ (30%). At the same time, 0.7797 g La (NO ₃ ) ₃ · 6H ₂ O, 0.5353 g Eu (NO ₃ ) ₃ · 6H ₂ O and 1.8419 g citric acid in 40 ml of water were prepared and the blue tungstic acid solution Add to. The blue solution is dried in a vacuum drying shelf, initially forming a blue foam, from which a blue powder is finally produced. The solid is then calcined at 600 ° C. for 5 hours.

Example 9: Preparation of red phosphor (Gd _0.6 Eu _0.4 ) ₂ (WO ₄ ) _1.5 PO ₄ 2.2 ml gdCl ₃ x6H ₂ O and 1.465 g EuCl ₃ x6H ₂ O in 100 ml Dissolve in ethylene glycol (Solution 1).
1.73 g Na ₂ WO ₄ is dissolved in 70 ml H ₂ O (solution 2).
0.74 g K ₃ PO ₄ is dissolved in 70 ml of ethylene glycol (solution 3).

100 ml of solution 1 is first introduced into the conical flask. First, 70 ml of solution 3 is added thereto. The solution becomes cloudy but becomes clear again after stirring for a short time. A mixture of 70 ml of solution 2 and 5 ml of NaOH solution (1M) is then added dropwise.
The reaction mixture is transferred to a three neck flask and heated under reflux with stirring for at least 6 hours.
250 ml of acetone is added dropwise to the reaction solution. The precipitate is then removed by centrifugation and washed again with acetone.
The product is then calcined at 650 ° C. in an oven for 4 hours.

Example 10: Preparation of green-emitting phosphor Ba ₂ SiO ₄ : Eu 390 g of barium carbonate, 3.5 of europium (III) oxide, 63 g of silica gel (SiO ₂ ) and 5.4 g of ammonium chloride were mixed by grinding. To do. The mixture is calcined at 1100 ° C. in a CO atmosphere for 8 hours. After fine grinding, an additional 5.4 g of ammonium chloride is added and mixed well to produce a uniform mixture. The mixture is then fired again in a CO atmosphere at 1200 ° C. for 14 hours. After grinding, the powder is washed with water to remove excess halide and dried in air.

Example 11 Preparation of Green Luminescent Phosphor Lu ₃ Al ₅ O ₁₂ : Ce 537.6 g ammonium bicarbonate is dissolved in 3 liters of deionized water. Dissolve 205.216 g ammonium chloride hexahydrate, 228.293 g lithium chloride hydrate (xH ₂ O) and 3.617 g cerium chloride hexahydrate in about 400 ml deionized water and rapidly carbonize. The pH must be maintained at 8 by adding dropwise to the hydrogen solution and adding concentrated ammonia during this addition. The mixture is then stirred for a further hour. After aging, the precipitate is removed by filtration and dried in a drying cabinet at about 120 ° C.

  The dried precipitate is ground and then calcined in air at 1000 ° C. for 4 hours. The product is then ground again and calcined at 1700 ° C. in forming gas for 8 hours.

Example 12: Manufacture of LEDs and installation in a liquid crystal display The phosphor from Example 10 (green phosphor) and the red phosphor from Example 6 in a mixing ratio of 1: 2.17 for both A and B manufactured by Dow Corning In the silicone resin system OE6336, mixing is performed with the aid of a tumble mixer so that the phosphor concentration in the two components A and B is 10% by weight. 2.2% by weight Merck silica gel powder is then added to both mixtures in order to make them thixotropic and the resulting mixture is homogenized again in a tumble mixer. 5 ml of component A and 5 ml of component B are mixed in each case to produce a homogeneous mixture and introduced into a cartridge connected to the dispenser metering valve. A COB (chip on board) crude LED consisting of a bonded InGaN chip with a surface area of 1 mm ² and emitting a wavelength of 450 nm is fixed in a dispenser. Domes are placed on each chip by XYZ positioning of the dispenser valve. The dome consists of two silicone components and two phosphors made thixotropic and a silica gel powder mixture. The COB-LED thus treated is then brought to a temperature of 150 ° C. at which the silicone solidifies. The LED can then be activated and emits white light having a color temperature of 6000K. Several of the LEDs produced above are then installed in the backlight system of the liquid crystal display.

Claims (17)

  At least one comprising at least one semiconductor diode and a combination of at least two phosphors, wherein at least one phosphor emits red light and at least one phosphor emits green light. A liquid crystal display comprising a backlight system having at least one white light source, comprising: The white light source includes a light emitting indium aluminum gallium nitride semiconductor, in particular ones represented by the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1 The liquid crystal display according to claim 1.   The liquid crystal display according to claim 1 and / or 2, wherein the white light source comprises a blue-emitting InGaN semiconductor.   4. The liquid crystal display according to claim 1, wherein the phosphor layer includes a europium (III) or chromium (III) activated line emitter as a red light emitting phosphor. 5. Phosphor layer, as a red-emitting _{phosphor, Al 2 O 3: Cr,} Na 0.5 Gd 0.3 Eu 0.2 WO 4, Na 0.5 Y 0.4 Eu 0.1 MoO 4, Na 0 _{.5 La 0.3 Eu 0.2 WO 4,} Na 0.5 La 0.3 Eu 0.2 MoO 4, Na 0.5 La 0.3 Eu 0.2 (WO 4) 0.5 (MoO 4 ) _0.5 , La _1.2 Eu _0.8 MoO ₄ , La _1.2 Eu _0.8 WO ₄ , (Gd _0.6 Eu _0.4 ) ₂ (WO ₄ ) _1.5 PO ₄ 5. Liquid crystal display according to claim 4, characterized in that it comprises selected europium (III) or chromium (III) activated line emitters.   The phosphor layer includes, as a green light emitting phosphor, a cerium (III) or europium (II) activated phosphor selected from the group of thiogallate, silicate, oxonitridosilicate, aluminate, nitride or garnet The liquid crystal display according to any one of claims 1 to 5.   A backlight system having at least one white light source comprising at least one semiconductor diode and at least one phosphor layer comprising a combination of at least two phosphors emitting red and green light. The white light source includes a light emitting indium aluminum gallium nitride semiconductor, in particular ones represented by the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1 The backlight system according to claim 7.   9. The backlight system according to claim 7, wherein the white light source includes a blue light emitting InGaN semiconductor.   10. The backlight system according to claim 7, wherein the phosphor layer includes europium (III) or chromium (III) activated line emitter as a red-emitting phosphor. 10. When the phosphor layer is a red phosphor, Al ₂ O ₃ : Cr, Na _0.5 Gd _0.3 Eu _0.2 WO ₄ , Na _0.5 Y _0.4 Eu _0.1 MoO ₄ , Na _{0. 5} La _0.3 Eu _0.2 WO ₄ , Na _0.5 La _0.3 Eu _0.2 MoO ₄ , Na _0.5 La _0.3 Eu _0.2 (WO ₄ ) _0.5 (MoO ₄ ) Selected from the group of _0.5 , La _1.2 Eu _0.8 MoO ₄ , La _1.2 Eu _0.8 WO ₄ , (Gd _0.6 Eu _0.4 ) ₂ (WO ₄ ) _1.5 PO ₄ 11. A backlight system according to any one of claims 7 to 10, characterized in that it comprises an activated europium or chromium activated line emitter.   The phosphor layer includes, as a green light-emitting phosphor, a cerium (III) or europium (II) activated phosphor selected from the group of thiogallate, silicate, oxonitridosilicate, aluminate, nitride and garnet The backlight system according to any one of claims 7 to 11. Blue-emitting indium aluminum gallium nitride semiconductors, particularly those of the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1, and emit red and green light A white light source comprising a phosphor layer comprising a combination of at least two phosphors.   The white light source according to claim 13, comprising a blue light emitting InGaN semiconductor.   15. The white light source according to claim 13 or 14, wherein the phosphor layer includes a europium (III) or chromium (III) activated line emitter as a red light emitting phosphor.   The phosphor layer includes, as a green light-emitting phosphor, a cerium (III) or europium (II) activated phosphor selected from the group of thiogallate, silicate, oxonitridosilicate, aluminate, nitride and garnet The white light source according to any one of claims 13 to 15. A method of manufacturing a liquid crystal display including a backlight system having a white light source, the following steps:
Blue light emitting InGaAlN semiconductors, in particular those represented by the formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k and i + j + k = 1, and red light emitting phosphors and green light emitting phosphors Producing at least one LED constructed from phosphor layers comprising a combination of:
Providing a backlight system including a diffuser and a reflector by installing one or more LEDs in a housing;
Combining a backlight system with a corresponding liquid crystal unit including a front plate having a color filter system to provide a liquid crystal display;
Including said method.

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